Circuit boards on which various components are mounted have been widely used for electronic devices. For example, it has been known that an electronic device (a semiconductor package) includes a circuit board (a package substrate) on which a semiconductor element is mounted, or an electronic device includes a circuit board, such as a mother board, on which a semiconductor package is mounted. As the operation speed of electronic devices has increased, a differential transmission type circuit board as a circuit board has been used, signals in the differential transmission type circuit are transmitted through a pair of transmission paths.
Japanese Laid-open Patent Publication No. 2001-203470 and Japanese Laid-open Patent Publication No. 2010-192767 are reference documents.